Flying head with foil support

ABSTRACT

Disclosed is a novel flying head supported on a stationary, rigid arm to present a &#34;hydrodynamic&#34; head-face to a passing flexible record segment, the segment being induced by this face to automatically assume a prescribed, relatively controlled configuration and spacing relative to the head-face.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Ser. No. 63,755, filed Aug. 6, 1979 for"Flying Head With Foil Support", now issued as U.S. Pat. No. 4,330,804,and of the Parent thereof U.S. Ser. No. 48,701, filed June 15, 1979 for"Flying Head With Compound Foil" (now abandoned), both cases by DeanDeMoss and both commonly assigned.

INTRODUCTION

This invention relates to structures for "non-contact" magneticrecording and more particularly relates to improved "flying-head"transducers and associated techniques for such recording.

BACKGROUND, FEATURES OF INVENTION

Workers will recognize that various techniques are known for confrontingmagnetic recording media with a magnetic recording transducer face. Forinstance, according to one technique, the transducer face is broughtinto contact with the passing medium. According to another technique("non-contact" recording) the transducer face is virtually "flown" abovethe medium and kept out of contact therewith as a guard against damageto the medium, to the face or to both. Generally speaking, workersprefer such "out-of-contact" techniques where feasible. This inventionconcerns an improvement in "non-contact recording" and an associatednovel configuring of the transducer face.

Magnetic memory storage units are a significant item of peripheralequipment in today's computers. In the typical unit data is stored onone or several magnetic disk drives. Such a drive will be recognized ascharacterized by one or more rotating magnetic recording surfaces onwhich data may be written, and read back, by a magnetic tranducermounted in a recording head. Such heads are "flown" in close proximityabove a recording surface. Great care is taken that this flying headnever "crashes" against the disk since catastrophic damage to both canresult. Yet, to maximize recording density and optimize signal/noise,workers know that the "head spacing" (spacing between the head-face, andcore there, and the surface of the moving disk) must be kept as small aspossible and be held within very tight tolerances.

It is common to establish "head spacing" for a "flying head" byconfiguring the head-face in the fashion of an "air bearing" whileestablishing the proper fluid dynamics. The magnetic head surface is,today, mounted on a resilient suspension and urged toward the surface ofthe moving disk by a head actuation means, but is prevented from actualdisk contact by an intervening cushion of air--called a "Bournoullifilm" and established as the air bearing. Once this Bournoulli film isdeveloped, it presents a rather substantial hydrodynamic resistance toreduction of "head-spacing" and significant force must be exerted topush the head closer to the disk. But certain abnormal conditions candisturb this "Bournoulli film" and suddenly remove it as a protectivecushion, sending the head crashing into the disk. Thus, workers in theart are very meticulous in developing the proper (aerodynamic) headfaceconfiguration and in positioning the head so as to properly orient it(e.g., re pitch and roll angles) relative to the passing disk such closetolerances that a change of a minute of arc or so can be critical!

Workers know that it is critically important to maintain a predictableconstant "head spacing" over a wide range of operating parameters ifmagnetic recording is to be successful. Head spacing is particularlycritical with high density recording--e.g., it can vary the "fringingflux" pattern and affect read/write resolution.

The foregoing relates, mainly, to rigid media technology and--as workersare beginning to realize--is not necessarily applicable to flexibledisks. This invention is particularly concerned with improved transducerconfigurations especially adapted for "near-approach" to floppy diskmedia during read/write sequences.

Workers also know that there are many factors affecting head spacing;such factors as the speed, configuration "penetration" andradial-position of a head [understand: "head speed" as the relativevelocity between medium and transducer and "head penetration" as thepenetration of the transducer stabilizer combination into the plane ofthe passing record medium, causing the latter to "dimple"]. Otheraffecting factors are disk characteristics (e.g., flexibility,thickness, etc.) and ambient conditions such as temperature andhumidity.

Early Efforts

Until recently, workers have been very uncertain as to how to present(mount) a (R/W) transducer means in operative relation with a passingflexible medium, like a floppy disk. Little guidance was afforded byexperience with conventional (digital magnetic recording) tape becausethis medium moved comparatively slowly and in contact with itstransducer head, with bit-density being relatively less critical."Flying" a head relative to tape was not practically contemplated, oreven thought necessary.

And the rigid disk technology was not too helpful. For instance,"Winchester" type heads typically used to over-fly spinning rigid diskmedia were tried with floppy disks--and results were disastrous, withhead crash quite common!

Attempts were also made to configure known head arms, or "paddles",(which commonly carry a "R/W head" into operative relation with rigiddisks--e.g., see arm A, FIG. 2A) to "fly" relative to floppy disks butwith no real success [e.g., distal end of paddle shaped like "air-foil"or made cone-shaped--with, or without a "head" mounted thereon]. Alsotried was a rigid "paddle" carrying a conventional R/W head button whichwas, in turn, mounted on a certain "pedestal"--e.g., a cylindrical-nosedpedestal or a "concave-sided mesa" type pedestal. Neither approachpromised success. But--when such a rigid "pedestal" was re-configured topresent a prescribed kind of spherical face to the approaching disksurface--according to a feature hereof--success hove into sight!Anobject hereof is to teach such a novel head-support combination.

Now, it is preferred here that a transducer be thrust to "penetrate" and"dimple" the flexible medium, and so better assure that head spacing bekept constant. However, such a "dimpling" can cause problems. Forinstance, it may degrade the desired film (Bournoulli) at the diskperiphery and cause "flutter" there to upset the prescribed headspacing. Such problems have, to date, limited the useful recording areaadjacent a disk's periphery, as workers well know. The present inventionis adapted to help in maintaining constant head spacing by eliminating,or at least alleviating, the mentioned problems and so improvingdisk-head stability--particularly for "flying heads" adapted totransduce for a pack of floppy disks (rather than one disk). In suchcases, there will be no "backing plate" (Bournoulli plate) as istypically used with a "single floppy" [e.g., IBM U.S. Pat. No. 4,074,330mentions that a problem with such Bournoulli plates is that head spacingdecreases as the head moves radially out on the floppy disk--and triesto solve this problem].

Now, the trend today is to record at ever higher "bit densities" (thatis, to record individual data transitions that are closer together).And, as bit densities increase, one must reduce the "head spacing" moreand more, as workers well know, (also, signal strength increases as headspacing drops). Thus, the task of configuring a head face to create theproper Bournoulli film becomes ever more critical with today's advancedhigh-bit-density equipment where head spacing on the order of just a fewmicroinches is not uncommon.

This problem is greatly aggravated when one uses flexible disk media(floppy disks). As workers well know, it is not uncommon for such disksto develop surface undulations approximating several dozen microinchesunder high speed rotation.

Progress toward the more effective use of high speed flexible disks inrecording systems is facilitated by a better understanding ofstabilization requirements. Some workers, [see articles by R. Benson, D.Bogy in J. Appl. Mech., Vol. 45, p. 636 (1978); and by H. Greenberg,IEEE Trans., Vol. Mag-14, 5 (1978)] have studied the overall response toa localized load on a flexible disk. Greenberg (above) describes thehead/disk interface with an expression that uses Reynolds equation forloading. This invention is directed toward establishing improved headsurface geometry as a means of optimizing flying characteristics; andespecially for providing stable, relatively uniform air bearing spacingsin the sub-micron region at higher surface speeds (e.g., 40 m/sec.). Itis an object of the present invention to develop a novel headconfiguration adapted to provide a proper "Bournoulli film" cushion whenemployed with flexible disks under high speed rotation, especially fortransducing at high bit densities.

The use of flexible magnetic recording disks as a storage medium in anenvironment requiring high linear speeds has necessitated the design ofair bearing contours which can provide reasonable wear characteristicsat stable, sub-micron spacings. Unlike rigid disk sliders, thesebearings must cope with the flexible nature of the disk as well as withthe gas pressure forces which support it.

Several means for supporting a flexible disk in close proximity to arecording transducer have been discussed by workers in the art. I.Pelech and A. Shapiro [see J. Appl. Mech., Vol. 31, p. 577, 1964]; andP. Charbonnier [see IEEE Trans., Vol. MAG-12, 6, 1976] have discussedthe possibility of a head fixed in a stationary plate, near which aflexible disk is rotating. The air film which develops between the plateand the disk serves to stabilize the disk in the axial direction.Charbonnier also suggested the use of a forced air nozzle to locallysupport the disk in the vicinity of a recording head.

The transducer may also be supported by an air bearing on the side ofthe disk opposite the stationary stabilizing plate. This approachfacilitates radial motion of the head in order to access written trackson the disk surface. The instabilities associated with the applicationof a stationary, localized load to a flexible disk supported in thismanner have been analyzed by Benson and Bogy (article cited above), whoprovide a description of the disk response. Although this lattersolution addresses the head/disk interface as well as the disk motion,the spacings developed are not adequate for high density digitalrecording.

This invention addresses the design of a suitable air bearing for usewith a rotating flexible disk. The disk in this configuration is one ofmany co-rotating flexible mylar disks which are separated by thinspacers through which air is permitted to pump naturally, outward in theradial direction. The air bearing spacing is thus controlled by thepressure forces resulting from the self-acting gas film, opposed by theforces exerted by the disk and by the air flowing behind it. Thisbearing must maintain a uniform, stable, predictable spacing between themagnetic transducer and the media, while minimizing wear between the twoadjacent surfaces. The dynamic stability of the disk must also bepreserved.

Fixed head versus movable head:

It is conventional to design a computer disk file so that its flyingrecording heads are "movable" rather than "fixed". When operation beginsand the disk surface is spun-up to the proper operating speed, therecording head is advanced, being pressed toward the disk to a "finalfloat" position--close enough to generate the desired air bearing(Bournoulli film). Such a "flying head" may later be retracted when thedisk is stationary (or rotated at low rpm) as desired (e.g., when"read/write" is completed). The technique used in bringing the head from"retracted" to "final float" position is commonly referred to as"landing" the head (even though there is no physical contact with thedisk). This invention relates to "fixed" heads, and to techniques forpromoting a more stabilized "final float" condition.

An example of a movable recording head is seen in U.S. Pat. No.3,310,792 to Groom, et al. Here, a resilient gimbal spring is providedto suspend a magnetic recording head adapted to float on an air-filmadjacent the surface of a rapidly moving memory disk. This gimbal springcan withdraw the head from the "float" position (e.g., see FIG. A) to"retracted" position (e.g., compare FIG. B) whereat the spring is in itsneutral, or unstressed, condition. Advancing the head (e.g., via adriving pneumatic piston) back to "float" position, stresses the spring.Besides mounting the recording head for advancement and retraction, thegimbal spring also accommodates proper head orientation --exerting avery small moment on the head so that in "retracted" position, its "toe"(or leading edge) is further from the disk than its "heel" (or trailingedge)--whereas when in the "final float" position, the Bournoulli filmdeveloped will rotate the head somewhat so that its "heel and toe" aremore nearly equidistant from the disk (compare FIGS. A and B).

Now, during "landing" there is a danger of the heel contacting the disk,with the toe being pitched-up unless a significant Bournoulli film hasbeen generated. In the past this problem has been addressed via acompromise between minimizing head spacing and optimizing read/writeefficiency vs. emphasizing a "safe" landing mode (i.e., with too close aspacing, there is a high risk of "crash", whereas too great a spacingwill degrade recording characteristics). This problem is addressed and,to an extent, solved by techniques taught by U.S. Pat. No. 3,678,482 toBillawala, discussed below.

Prior art head manipulation; FIGS. A, B:

FIG. A illustrates a typical prior art recording head 16 understood as"flying" adjacent a recording disk 17 in its "final float" position.(See also, U.S. Pat. No. 3,678,482 for further details). As illustratedhere, disk 17 will be understood as moving from right to left, withconstruction and operation being carried out conventionally except asotherwise specified. In its "final float" position, the recording head16 floats with its heel end 19 at a minimum distance H from the surfaceof disk 17 and its face 21 tipped-away very slightly (or "pitched-up" bya very small angle θ) so the forward projection of face 21 (i.e., bevelface 22 adjacent toe-end 18) is tipped slightly further away from disk17, as known in the art. Face 21 is relatively flat and, beingpitched-up slightly toward the approaching recording surface; mergesinto the second flat face 22 beveled away from the record and divergingfrom face 21 by a prescribed relatively small angle α (--the trailingedge of face 22 thus coinciding with the leading edge of face 21, asillustrated).

It should be recognized, of course, that angles α and θ and distance h(as well as other like angles and distances set forth elsewhere herein)are greatly exaggerated for illustration purposes as compared withactual scale. Thus, for instance, in the prior art fluid film bearingillustrated in FIG. A distance h will preferably be on the order of afew dozen microinches and angles α and θ on the order of a few minutesof arc.

As workers know it is conventional for a gimbal spring arrangement (notshown, but well known in the art) to be provided for suspending head 16and permitting the indicated orientation--the head being thrust towardand away from record 17 by a position arrangement 23 (not fullyillustrated, but constructed and operated as well known in the art).

Under certain conditions head 16 is retracted (e.g., when disk rpmdrops); conversely, the head may be advanced to "land" adjacent the diskfor read/write operations when disk rpm reaches "operating speed". Whenpiston 23 acts to so thrust head 16 it will be understood that a force Pis applied and a moment M set-up to overcome the (rather slight)gimbal-spring-moment and rotate the head to fly more parallel with thepassing disk surface (e.g., rotate head 16 from FIG. B to FIG. Aorientation). A counter-moment M is then generated by the fluid filmagainst both head faces; this made-up from a force F-1 acting throughthe center of pressure on the main face 21 and a force F-2 actingthrough the center of pressure on the bevel face 22. Thus, in "landing",it will be understood that pneumatic pressure applied via piston 23forces the head toward disk 17 (--starting from the "retracted" positionillustrated in FIG. B) to reduce angle θ and eventually wind up in the"final float" position indicated in FIG. A. During "landing", it will beunderstood that the gimbal spring will tilt toe end 18 upward so that ashead 16 is pressed toward disk 17, the heel 19 first approaches thedisk--at this point a force F-1, originating from the fluid film, willcommence to act on main face 21, pivoting heel 19 slightly away fromrecord 17. (There being little or no fluid film pressure then appliedupon bevel face 22 since it is still too remote from disk 17).

In the final phase of landing, it will be understood that the forcedistributed on head 16 is such that piston 23 must be located near theheel 19 (higher density air film then present). That is as the headapproaches "final float" position and head spacing decreases, the pointof application for piston 23 against head 16 moves closer to heel 19(this maintaining the desired angle θ for stable floating). With piston23 positioned nearer heel 19, the landing moment is reduced (smallermoment arm, so F-1 is lower) and care must now be taken to avoid a"crash" against record 17 (heel 19 could strike disk 17 beforesufficient balancing force F-1 is generated to pivot recording head intoits final floating position.

The foregoing description relative to FIGS. A and B will serve toillustrate typical characteristics and problems associated with priorart, "non-rigid" heads and call associated difficulties to mind. Headsarranged according to this invention avoid all such difficulties sincethey are mounted to be rigid (non-movable) and arranged to induce the(flexible) medium to, alone, make the necessary approach and "landing".This should help workers to better appreciate the advantages andcharacteristics of a rigid-mounted "compound foil" head according to theinvention--wherein no head positioning or alignment is required, butrather a simple presentation of the moving flexible disk so it willautomatically position itself in proper transducing relation with thehead core (as further discussed below). The operational advantages andthe manifold difficulties avoided will be self-evident to workersfamiliar with this art.

Prior art: difficulties in "following" floppy disk with movable headFIG. 1A:

FIG. 1A shows, very schematically, some of the factors involved inconfronting a flexible magnetic recording medium, such as a floppy disksurface M, with a "canoe" type head A-1. Here, disk M will be understoodas swept rotationally past the recording face of transducer head A-1which is understood as mounted on a prescribed flexible suspension(indicated very generally as spring means A-2 and well known in theart). Head A-1 is shown as taking the form of the well known "canoehead" tilted up a prescribed pitch angle (aa) from coplanarity with anidealized perfectly level contact-plane R--R along which medium M (theconfronting surface thereof) would ideally be swept. Medium M is givenan exaggerated 37 wavy" configuration, since, as workers well know, itis very, very difficult to maintain such a flexible record surface flatalong the prescribed plane R--R.

It will be recognized that in such an arrangement the head A-1 is "flownover the disk", its transducing face being urged compliantly towardsreference plane R--R for transducing on the disk. Also, means will beunderstood as provided to urge the surface of head A-1 close to mediumM, separate only by the Bournoulli air film of minute thickness, and tobe very precisely maintained for accurate repeatable recording. Asworkers well know, so locating the head and moving floppy medium soclose together and maintaining this precisely is akin to squeezing twospring-mounted foils together, as they pass one another at highspeed--all in all a very unpleasant, somewhat imprecise, balancing actthat can frequently go awry, with the result that read/write defects areintroduced. This invention avoids such difficulties by postulating arelatively rigid transducer head over which the medium is made tofly--rather than flying the head over the medium.

One of the problems in prior art arrangements, like that of FIG. 1A,where the head is flown over the medium, is in making the "air bearing38(intervening film) stiff enough to maintain head-disk spacing despitechanging factors. A related problem is to always maintain the pitchangle of the head constant relative to the approaching disk surface--andso mounting and driving the head mass that it closely "follows" thepassing, undulating surface of a floppy disk. This, of course, is a veryserious challenge since, when rotated at the usual high speeds, floppydisks can undulate and flop wildly. The frequency of these undulationsis often so high that the head-following mechanism cannot really"follow" and maintain the tiny head-disk separation (as little as a fewu-in.).

Another problem in so "following" floppy disks is that the head massmust really be made "ultra-light"--even so, it is difficult to find aspring system matched to the disk and to actuate it with the proper"following mechanism". Also, in any situation where a flexibly mountedhead is arranged to follow a floppy disk surface, extreme difficultiescan result from "feedback oscillations" often encountered. That is, anundulating disk can, for instance, cause sympathetic oscillations of thehead. And the head, which typically has a different resonant frequencythan the disk, will maintain these unwanted oscillations for some timebefore settling down--and may impact disks damagingly- On the otherhand, using a rigid head, as in this invention, will lower the "Q" ofthe flexible medium and can damp-out such unwanted vibration.

The foregoing problems are exacerbated when operating a floppy disk inthe desired "steep dive" mode whereby disk and head normally fly at arelatively large interspacing, with this being suddenly reduced as thehead approaches the recording zone on the disk--then, the head divessteeply toward the disk (or vice versa) and is removed therefrom just assuddenly when the recording zone is passed (the head climbing steeplyaway from the disk). Such "steep dive" mode presents serious risks ofdamage to head, or to the disk or both, since a "crash" is much morelikely under these conditions, with the stiffness of the air-bearing(Bournoulli film) varying widely thewhile. The present inventionsimplifies this situation greatly by making it unnecessary to "dive thehead" toward the disk--rather it aerodynamically "sucks" and holds thedisk (recording zone) closer to the rigidly-mounted head face (quasi"dash-pot" effect).

Invention features:

This invention avoids the problems suggested above by mounting the headrigidly and inducing the passing disk segment to fly over the head in aprescribed manner. So doing, there is no need for spring-mounting thehead, nor for related sensing and actuator mechanism to move therelatively large transducer mass. Rather, one simply developsaerodynamic forces that constrain the (relatively low mass) disk to"fly" at the proper height above the transducer core, with no need to"follow" the disk surface, as well as advantageously using a relatively"self-leveling" structure (the rotating floppy disk) to reference on afixed stable surface (the rigidly-mounted transducer face).

Thus, as one feature of novelty, the present invention involves flying aflexible disk over a rigid head with the head face configuredaerodynamically to induce a rather "steep mode" of confrontation,preferably, and involving a "compound curvature" configuration. (cf asmall "lens" atop a large "lens"). In a related feature, a prescribedspherical head-foil is mounted atop a relatively flatter sphericalmount-foil such that the stabilization-zone of the head-foil is keptwithin the (larger) stabilization-zone of the mount-foil, and morestabilized transducing promoted.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated by workers as they become better understood by reference tothe following detailed description of the present preferred embodiments.These shoould be considered in conjunction with the accompanyingdrawings, wherein like reference symbols denote like elements;

FIGS. A and B are schematic elevations of a prior art transducer head in"final float" and "landing" position, respectively, relative to apassing record medium;

FIG. 1A is a very schematic elevation of a prior art transducer flexibledisk arrangement;

FIG. 1B is a schematic elevation showing a flexible disk passing over a"single foil" configuration; with FIG. 1C showing the same in plan view;

FIGS. 2A and 2B illustrate a preferred "compound-foil" recording headembodiment in plan view and side-view respectively; while FIGS. 3A, 3B,3C are enlarged orthogonal side elevations of the same as confronted bya passing flexible medium segment, seen from two perspectives at rightangles to one another;

FIG. 4 is an enlarged plan view of the head in FIGS. 2 and 3 asconfronted by a passing medium;

FIG. 5 is a simplified side view of the general foil supported buttonembodiment;

FIG. 6 is a plot of head-disk spacing as a function of inter-slotposition and slot width;

FIG. 7 is a plot of minimum head-disk spacing as a function of headradius; and

FIGS. 8 and 9 are representations of head-disk spacing in terms ofoptical interference patterns.

DESCRIPTION OF PREFERRED EMBODIMENTS

General principles with "single-foil" head, FIGS. 1B, 1C:

Workers in the art are familiar with the principles whereby, in "flying"a flexible medium over a relatively spherical "foil" surface, a"Bournoulli air film" is developed--the thickness of the film beingdependent upon the relative velocity between the foil and the disk, thestiffness of the medium, and the spherical radius of the foil (t_(BF),v, K_(m), R_(f)). Such an arrangement is very schematically indicated inFIG. 1B which a relatively spherical foil F-1 having a radius of about 6inches (R-1) will be understood as overflown by a flexible disk medium Mat several hundred ips or more surface velocity, assume about 3000 rpmfor 15 in. disk--such that a Bournoulli air film of thickness t_(BF) isdeveloped (assume a 1.5 mil thick disk with a Bournoulli film thicknesst_(BF) of about 1/2 mil--this varying slightly with the disk radius).

Now it is found, quite interestingly, that such an arrangement cangenerate a stabilized "approach zone" Z, where disk foil separation is aminimum and is relatively constant (under proper conditions)--the sizeand shape of the zone varying with foil radius and "foil penetration"(i.e., the dimpling or deflection of the flexible medium by the head).

Such a zone Z is indicated in FIG. 1C wherein the foil F-1 of FIG. 1Bwill be understood as mounted to confront medium M (being swept past asin FIG. 1B). Such a zone Z will typically take an elliptical shape formost portions of a passing floppy disk (as illustrated in FIG. 1C andfurther explained below), this shape being characterized by diametersD₁, D₂, as illustrated. It has been found tht the average diameter D_(a)(D_(a) =D₁ +D_(2/2)) or the average zone area, roughly speaking, willvary with foil penetration. But this dependence varies, in turn, withfoil radius. Zone area will be observed to change relatively little withincreasing foil penetration for a relatively "steep" foil transition(i.e., small radius foil, e.g., 1 to 2 inches, with penetration from 10to 20 mils)--whereas it changes much more with increasing foil radius(that is, as the foil gets flatter, stabilized zone Z increases in sizeconsiderably as penetration increases--this attributed to diskstiffness, impeding "sharp turns" by disk).

The elliptical form of zone Z is believed due to an asymmetry in tensionforces actong on the medium adjacent--that is, in many instances, thetension across the plane of the disk will be high in the radialdirection (stretched), but relatively low in the direction of travel(less peripheral stretching, except at the edge of the disk)--thisserving to resist the spread of stabilized zone Z in the radialdirection D₁ but resisting it relatively little in the peripheraldirection D₂ as postulated in FIG. 1C. Such a stabilized zone Z for theabove-mentioned foil of FIG. 1B will be found in certain conditions toexhibit diameters of about 0.8 inches and 1.0 inches, being relativelyelliptical as indicated in FIG. 1C.

Now, it has been found--quite surprisingly--that such foils can be madeand operated so that such a zone Z maintains a relatively constantfoil-medium separation t_(BF) despite minor undulations of the mediumand despite penetration changes--i.e., the medium "follows" the foil(zone area) even as the foil is moved further toward it. For instance, arelatively "flat" foil, with a radius of about 12 inches, has been foundto hold a minimum foil-disk spacing of about 0.75 mils, despite a shiftin "foil penetration" from about 10 mils to about20 mils--this varieswith foil radius, however. And, with a relatively "steep" foil, having aradius of about 1.6 inches, the foil-disk spacing has been kept constantat about 0.25 mils over the same 10 to 20 mils variation in foilpenetration.

Accordingly--according to a feature hereof--it is proposed that ahead-foil be mounted atop such a "mounting foil", in this "approachzone" Z thereof, of constant flying height (as below). One may cause thedisk to fly over the head in that zone, being operated so as to maintainthe Bournoulli thickness despite minor variations in "foil penetration"(e.g., caused by manufacturing or assembly variances). Such a "two foil"array is discussed below and rather generally indicated in FIG. 5.

As was treated in the aforementioned studies by Bogy and Benson and byGreenberg, wavelike instabilities occur on the disk surface as a resultof the application of a stationary, localized load. If allowed to occurnear the magnetic transducer, these disturbances will cause undesirablemodulation of the signal. In order to smooth and stabilize a region ofthe disk adjacent the transducer, a spherically shaped "foil" isprovided according to the invention and is loaded against the disksurface, as shown in FIG. 5. This foil, which is larger in both diameterand spherical radius than the button supporting the tranducer, forms aself-acting air bearing, separated from the disk by approximately asuitable distance (e.g., 12.5 um preferred here).

Experience has shown that sharp corners, or even small radiused regions,are undesirable in the vicinity of an oxide-coated mylar disk, largelybecause of the accelerated wear which can result. The use of a spherical"slider", or head button, similar to the foil only of smaller diameterand spherical radius, presents a smooth surface to the disk. Material isthus recessed from the disk surface in each area except in the center,where the read/write transducer will be located. Optimization of bothfoil and button geometries, and control of the disk/transducer spacing,may be accomplished using stroboscopic white-light interferometry (withglass lens foil and head). An ideal air bearing design will provide astable interface dimension between head and disk, and white lightinterference affects will yield color values corresponding to thevarious film thicknesses that are observed.

FIG. 9 shows the interference-contour pattern obtained for a sphericalair bearing geometry at the typical surface speed and load. This is atypical fringe pattern for a spherical head button (here, radius ofcurvature=3.8 cm.; assume monochromatic light at 0.59 um wavelength usedfor photographic clarity). FIG. 9 is a reproduction from a static photoand simulates the pattern obtained with disk moving in direction of thearrow.

The curvature of the head surface provides relief from the disk in alldirections, while achieving the desired closer spacing in the centerregion. It is interesting to note how the center of the "flying bubble"dimpling the passing floppy disk, is displaced rearward from thegeometric center of the head surface; evidently due to the divergingflow, and resultant negative pressure in this region. Althoughsub-micron head-disk spacings suitable for magnetic recording can beobtained in this manner, there are difficulties which make thisconfiguration less than optimum. The amount of penetration into the diskthat is required to achieve usable spacings is quite large, and mayresult in undue wear between disks, or in other dynamic disturbances. Inaddition, the location of the region of closest spacing is relativelysensitive to head attitude with respect to the disk surface, and fallsoff quite rapidly in all directions from this location.

To a certain degree, the head-disk interface geometry can be controlledby changing the radius of curvature of the head. As indicated in FIG. 7,reducing head radius, and thus relieving the head contour from the disksurface, results in a smaller head-disk spacing at the minimum point.The foil, with a 15 cm curvature, would support a spacing ofapproximately 12.5 um, thus providing an upper limit for the curve.Although curvatures of approximately 1.9 cm and less provide suitableminimum head-disk spacings, the aforementioned difficulties indicate aneed for some further means of controlling the interface geometry.

"Two-foil" head embodiment; FIGS. 3A, 3B:

As a feature of this invention it is postulated that a transducer headbe mounted, somewhat conventionally in a first foil structure, then thisfoil be mounted, in turn, atop a second, flatter, (mounting-)foil of thetype discussed above (well within the approach zone Z thereof)--thisresulting in a "compound foil", or "compound lens", head configuration.It is found that with such a "compound foil" head, the disk willestablish its own flying height and will execute a "two-step"head-approach--i.e., will decend toward the mounting-foil as above (toestablish approach zone Z); then, within zone Z, will dive steeplytoward the head's "recording zone ZZ and return steeply therefrom, as isgenerally indicated in FIGS. 3A and 3B.

Here, it will be seen that the transducer foil F-H comprises arelatively spherical head-foil section mounted atop a "mounting-foil"F-1, as above mentioned, so as to induce a passing floppy disk segment Mto assume an approach zone Z of stabilization as in FIG. 3A togetherwith a secondary, "transduce zone" ZZ (above F-H). Head foil F-H isdisposed within the ambit of this stabilized zone Z with its outerradius blending with the peak surface of F-1. An "edge-foil" annulus F-2surrounds F-1 to minimize disturbance to a passing Bournoulli air film.The edge foil (or blending foil) F-2 is believed necessary to eliminatesharp transitions and flow discontinuities, thus minimizing anyresultant disturbance of the desired laminar Bournoulli flow andavoiding consequent air turbulance and drag.

As a subsidiary feature it is also preferred that head foil F-H beprojected well beyond the passing Bournoulli film. That is, the apex ofhead foil F-H will protrude well into the plane of medium pasage, pastthe Bournoulli film t_(BF) (about 1/2 mil in the subject example). Insuch a case it is found --quite surprisingly--that the passing disk willgently rise and overfly this "secondary lens" protrusion (F-H) quitereadily. Now--again, surprisingly--the flying height of the disk as itthus passes over head F-H is somewhat greater than that established bythe head foil F-H, by itself (in the absence of foil F-1). Also,surprising: while increased "foil-penetration" increases the area of themajor stabilized zone Z, it doesn't significantly change head-spacing(flying-height) over head foil F-H, (FIG. 3B shows this).

For example, assuming a head-foil radius of 1.6 in., it will be seenthat the head-foil alone would induce a Bournoulli film thickness ofabout 0.2 mils; whereas, as above noted, the mounting foil F-1 by itselfinduces a Bournoulli film thickness of about 0.5 mils. Now, whencombining these two foils in a "compound" (two-foil) configuration (thatis, mounting the steeper foil F-H upon head foil F-1), the Bournoullifilm passing over F-H was only about 0.25 mils thick (in head zone Z';see FIG. 3B, spacing t₂ =0.25 mils; t₁ =0.50 mils).

In other words, as the air film established by the foil passes the headit will be observed to be partly deflected around the center of the headnode, inducing the disk to fly at a lower height, there, than thatheight established by the mounting foil alone. This air film,established in zone Z' adjacent the apex of head foil F-H, might becharacterized as a "second order Bournoulli film"--i.e., a thinner airbearing, resulting when a given foil is surmounted with a "steeper"foil.

Head slotting; FIGS. 8, 3C:

Also, with this "compound curvature" reducing Bournoulli film thicknessabove head-foil F-H it would still be desirable to reduce head spacing(e.g., to a few u-in.) above the small recording zone adjacent the cores(on F-H). That is, it is very desirable that after the disk has enteredzone Z' it be induced to "dive steeply" toward the core region atop F-H;and then return quickly after passing the cores--reducing head spacingto a few u-in. thus, establishing a transducing zone CR (FIG. 4;modifying FIG. 3B by radically reducing height T₂ to a few u-in.; i.e.,to height T₃ ; ZZ is width of zone CR, and can typically be "flatter"than zone Z', front-to-back, as FIG. 3C suggests; see FIG. 4 also).

Several alterations to the spherical head geometry were considered as ameans of controlling the pressure distribution in the air bearing. Theseincluded: flat tapers, secondary spherical radii, bleed holes, andlongitudinal slots. The latter method was thought relatively simple toimplement and, although the sharp edges of the slots raise some concernabout wear, the method was adopted and used successfully. Preliminaryexperiments with one, two and three slot geometries indicated apreference for two slots; the single slot head showed sensitivity tohead attitude similar to the unslotted head, while three slots werefound to offer no measurable advantage over the dual-slot pattern.

The general effects of the two longitudinal slots are quite favorable.As the two slots relieve air pressure in a region of the bearing, thelocalized loading is reduced, and the disk tends to wrap slightly aroundthe head contour in both longitudinal and transverse directions. Theresult, is that the region of closest spacing is more widelydistributed, and is well-controlled by the slot boundaries.

Further investigation has shown that the geometry of the head-diskinterface can be controlled by varying the "slot-to-slot" spacing(D_(s-s)) and/or the slot width (w_(s)) with slot width the moreeffective parameter. The result of varying slot width on interfacecontour is shown in FIG. 8. For wider slots, the disk is drawn towardthe slot, resulting in a potential wear problem near the slot edge. Thetransverse flow of air is also restricted, causing a "bubble" in thecenter section (of the disk). From the standpoint of wear, this isundesirable, since the minimum spacing is not located at a pointsuitable for transducer placement, and disk clearance is thusunnecessarily sacrificed. Reducing slot width in a controlled fashionpermits control of the final pattern, such that a smooth uniform contouris obtained. Using this approach according to the invention, it ispossible to compensate for changes in disk surface speed, and in diskproperties, while still maintaining reasonable interfacecontours--something rather unexpected.

Thus, we want to pull the medium much closer-in at zone CR. To effectthis a pair of like bypass grooves, or slots SL, (best seen in FIG. 3C)were cut along the direction of disk travel bracketing the core region.Such slots were found to reduce air bearing pressure in zone CR,modifying the effect of the compound curvature there and enhancing thedepressing effect of atmospheric pressure there (i.e., adjacent the headH, at the apex of F-H, so that, principally, the spherical radius R_(H)of the head foil F-H acts to control flying height in the core zoneCR--thereby establishing its own reduced-pressure air bearing filmthere, as indicated in FIG. 3C. (FIG. 3A is a like side view with thedisk segment assumed to move from left to right, while FIG. 3C is ahead-on view with the disk assumed moving into the plane of thedrawing).

Slots SL will be understood as disposed parallel to one another and tothe contemplated direction of medium passage, being spaced-apart adistance which will establish the width w_(z) of this core region,(e.g., see FIG. 3C). The slots are cut to a depth and cross-sectionsufficient to "bleed-off" enough passing air to allow the describedreduction in Bournoulli film thickness (here, for example, the thicknessis reduced from about 250 u-in. to about 2-15 u-in.) in a relativelysteep dive, or sharp transition, as mentioned above--yet not so much asto divert all the air and reduce film thickness to zero (lest the mediumcontact the head F-H, as workers will understand). Thus, slotcross-section can, to a large extent, control flying height T₃ over thecore region CR, and preferably (as here) is arranged to divertsufficient passing air that--in region CR--the influence of foil F-1 isremoved.

FIG. 4 is an enlarged plan view from above head-foil F-H of FIG. 3C.Here, it will be observed that a core C with a core gap C-g is apparentwithin the somewhat ellipitical shaped core region CR. The area ofregion CR should be made as small as possible, since one desires todisturb the passing minimally. It has been found that increased"loading" (force on the disk toward head) can increase the area (size)of outer stabilizing zone Z; yet with no change in the size or shape oftranducing zone CR--something quite surprising and significant (e.g.,leading to "isolation" of core-spacing from shifts in head-loading). Ofcourse, the perturbation caused by creating this approach zone Z will"dimple" a passing disk somewhat, throwing some energy into it andperhaps causing a secondary rippling-outward (e.g., in the downstreamdirection). This will be dissipated over a "settling down" time/space;the dimple-excursion should be minimized, of course, to resistinter-disk collision (collision with other disks in the pack, that ispossible due to sympathetic vibrations in certain cases). Moreover, thethe air bearing forces should be stiff enough so that the disks maycontinue to fly at their controlled altitude without impact betweenthemselves or with the head. (Note gap C-g defines zone width ZZ).

Interestingly enough, as noted in FIG. 4, the transduce zone CR takes arelatively elliptical shape, being biased slightly off-center, to thedownstream side of the head center-line CL (a few mils downstream andadjacent the core gap C-g, preferably, as indicated). The width ofregion CR is, of course, defined by the slots SL.

The "off-center" placement of region CR is believed due to the asymmetryin upstream-downstream forces, sucking the disk in toward the head onthe one hand and peeling it away on the other. That is, there isrelatively high "upstream" pneumatic resistance, vs. pulling the diskinward against the head; and there is usually a downstream suction(e.g., at times a partial-vacuum) opposing the peeling away of the diskas workers will understand.

In the following table Example I, summarizes an exemplary"compound-foil" head embodiment according to the invention along thelines indicated in FIGS. 2A, 3C and 4 and discussed above:

EXAMPLE I Exemplary Head with "Compound-Curvature"; (see FIG. 2B):

Spherical Mounting foil F-H: radius (R₁)=6"; dia. D₁ =1.1"

Spherical Head foil F-H: radius (R_(h))=1.6" dia D_(h) =0.3"

Mounted on paddle arm A, 40 mils thick; with back-foil F-3 raised 30mils (3" radius R₃) and outer, relatively "steep" edge-foil F-2 ofradius R₂ =3"; dia. D₂ =1.5" and F-H, F-1, F-2 projected total heighth_(h) =67 mils.

Pedestal F-2 is used only to thrust the transducer gaps atop F-H farenough into the floppy "dimple" and may vary in height according to thispenetration depth d_(p) desired.

Head slots SL: 6 mil wide flanking head H, extend the length of foilF-H, and as deep as F-H protrudes above F-1.

Core region CR thus formed: 10 mils wide (core-width)×50 mils long,yielding flying height T₃, above cores of about 12-15 u-in., and withload force of 25+ gm. (added load not change T₃ or zone CR; only changessize of stabilizing zone Z).

Head:

track width--10 mils

gap length--0.1 mil

throat height--1.3 mil

curvature--0.3" dia.; 1.6" radius (as above D_(h), R_(h)).

Results

A slotted "compound curvature" head of the type described above has beenoperated for many hours with remarkable stability and high qualityread/write performance, even at high bit density (e.g., 10,000 bpi). Forinstance, it has been run continuously, yet no oxide build-up on thehead or marking of the disk has been noted. This head can be used in"dual recording" (i.e., it can "look up or look down"); also it canaccommodate an ultrahigh medium velocity (up to about 1000 inches persecond--versus about 100 inches per second for the usual floppy).

Conclusions

It is evident from the above that, according to the invention, animproved "air-bearing" design is provided, one suitable for use in highdensity magnetic recording on flexible media. That is, surrounding thetypical "head button" with a relatively flatter foil, has been seen toradically affect the disk/head interaction--surprisingly so in view ofthe relatively minor change in head configuration. The pressure profilesin the air bearing can be controlled through the use of longitudinalslots, with the widths and placement of these slots influencinguniformity of head/disk spacing. Heads have been fabricated using 0.064mm wide slots with a 0.500 mm center section and a 3.8 cm radius ofcurvature, we have found signal modulation properties to be excellentand wear relatively negligible over several hundred hours of continuousoperation.

Workers will appreciate that this surrounding of a given head-foil witha mounting foil of prescribed leading-edge configuration (e.g., flattercurvature) can pull down a relatively large "dimple" in the passing diskand hold it somewhat "close" (e.g., here, order of V₄ ") to thehead-button carried thereon--leaving the bottom foil-shape (F-H) tothereafter reduce this flying height (T₂) still further in an inner"sub-dimple" (e.g. zone Z' within zone Z). Thus, this can superpose thelarger (major) stabilized zone Z of the flatter mounting foil about thesmall (minor) stabilization zone Z' of the head-foil--so thatperturbations of the approaching disk surface are absorbed by zone Zbefore reaching and affecting zone Z', and also smoothed-out downstreamof Z'--e.g., a ripple might increase head spacing hs at the leading-edgeof the mounting foil, but only cause a slight shift in the size of majorzone Z, leaving minor zone Z' unaffected and maintaining constant sizeand head spacing there. This is crucially important using floppy disksas workers well know.

Or, from a slightly different viewpoint: the important minor zone Z' canwork completely within a prestabilized outer zone Z and start from amuch-reduced flying-height, making it considerably more effective incontrolling the configuration of zone Z' (e.g., dive-location) and headspacing there (can hold closer tolerances more reliably). Slots or thelike, can further be added to reduce flying height still further (e.g.,at zone ZZ). And, of course, the configuration of mount-foil F-1 shouldbe kept "regular" at its "leading-face" where it will be approached bydisk surfaces from somewhat-varying quarters (e.g., approach angle alongradially-inner track different from that of radially-outer track); butmay vary from this along "trailing-face" portions where it need onlyhelp to "settle-down" to departing disk surfaces (e.g., sufficient tominimize turbulance, flutter, etc. before the revolution is completedand this disk-surface may once more pass the head F-H). For instance,workers may visualize other, different trailing-face configurations(e.g., elongate and streamlined as with an air-foil cross-section)serving this function. Also, radial-outward portions of foil F-1 mayvirtually be ignored (e.g., cut-off, if convenient) in many cases, aslong as the cited purposes of the leading and trailing-faces are served.Most of all, note that this leading-face configuration is "regular",presenting the same curvature to disk surfaces, no matter what theirapproach direction. Of course, convenience will often dictate making thefoil F-1 so it presents the same curvature in all directions, as inFIGS. 2A, 2B, etc.

It will be understood that the preferred embodiments described hereinare only exemplary, and that the invention is capable of manymodifications and variations in construction, arrangement and usewithout departing from the spirit of the invention.

Further modifications of the invention are also possible. For example,the means and methods disclosed herein may also be applicable to tapesystems and the like in certain cases. Also, this invention isapplicable with other "compound-foil" configurations and is useful inother forms of recording and/or reproducing systems.

The above examples of possible variations of the present invention aremerely illustrative. Accordingly, the present invention is to beconsidered as including all possible modifications and variations comingwith the scope of the invention as defined by the appended claims.

What is claimed is:
 1. A combined transducer-stabilizer array adaptedfor stabilizing and transducing passing flexible media, the combinationincluding a magnetic transducer structure disposed in at least oneprescribed head-foil means of given, "regular lead curvature" along allleading face portions so that said media may approach the foil meansfrom various directions and still confront a constant, regularhydrodynamic surface configuration; this foil means being presented inconvex, "air-bearing-generating" relation with said passing media and inrelatively rigid, stationary relation therewith, whereby to develophydrodynamic forces which constrain the media to "over-fly" the rigidfoil means and associated transducer structure at proper height levels;and arm means carrying said foil means so as to be so presented inrigid, stationary fashion.
 2. The combination as recited in claim 1,wherein the foil means exhibits one or more relatively spherical convexsurface configurations along said lead-face portions and is presented onsaid arm means so as to be injected a prescribed penetration distanced_(p) into the "plane" of the passing medium segments.
 3. Thecombination as recited in claim 2, wherein the trailing portions of saidfoil means are configured so as to minimize turbulance and mediumflutter and to quickly attenuate any medium disturbance.
 4. Thecombination as recited in claim 1, wherein said leading-face portionsare configured to "draw" passing medium portions toward themselvessufficient to establish a prescribed "transducer-spacing" S_(t) andassociated upstream "entry zone" relative to these passing mediumportions.
 5. The combination as recited in claim 4 , wherein saidleading face portions are so configured to also shape said "entry zone"to lead smoothly into a "transducer-zone" whereat said spacing S_(t) ismentioned relatively constant despite moderate changes in penetrationdistance d_(p) or in the mass per cm² of the media.
 6. The combinationas recited in claim 5, wherein the trailing portions of said foil meansare configured so as to minimize turbulance and medium flutter and toquickly attenuate any medium disturbance.
 7. The combination as recitedin claim 6, wherein said foil means is so configured as to generate arelatively elliptical transducer zone with its major axis along thedirection D_(r) of media travel.
 8. The combination as recited in claim7, wherein said foil means comprises a pair of superposed sphericalfoils adapted to induce the passing medium to approach sufficientlyclose to the transducer to induce a transducer height S_(t) on the orderof a few micro-inches or less.
 9. The combination as recited in claim 2,wherein at least one pair of relief means are cut into said foil meansat sites symmetrically flanking the transducer structure, those reliefmeans being arranged to reduce the flying height S_(t) of said passingmedium above the transducer structure and thus generate a prescribedtransducing zone while limiting the width of the zone, laterally of thedirection of media translation.
 10. The combination as recited in claim6, wherein is also included a pair of relatively identicalpressure-relieving relief means cut into the head-support meanssufficient to establish a prescribed relief and suction in saidtransducing zone, said relief means being disposed to symmetricallyflank the transducing zone and being aligned parallel to in thecontemplated direction of disk passage, also being dimensioned to reducehead spacing S_(t) to a prescribed amount.
 11. An improved transducerstructure adapted for presenting transducer head means in prescribednon-contact transducing relation with passing flexible recording mediawhich is relatively free-flying and unconfined relative to the head;saidstructure comprising head-supporting/medium-stabilizing foil means inwhich the head means is mounted and associated arm means adapted topresent said foil means and head means in rigid, stationary transducingrelation with the passing media yet thrust into the plane thereof aprescribed penetration distance d_(p) ; this foil means beingcharacterized by lead-face portions of a prescribed regularconfiguration adapted to generate a prescribed air-bearing on passage ofthe media so that it overflies the head means at a prescribed relativelyminiscule flying-height h_(f) and thus traverses a "transducer-dimple"path of prescribed configuration.
 12. The combination as recited inclaim 11, wherein said lead-face portions are also configured tointroduce an "entry zone" air film upstream of the head means.
 13. Thecombination as recited in claim 12, wherein said foil means is mountedatop pedestal means of height h_(p) sufficient to cause sufficientpenetration d_(p) of the head means.
 14. The combination as recited inclaim 13, wherein said arm means is cantilevered-out from base means andarranged and operated to so thrust the foil means into the plane of thepassing media segment a distance d_(p) as to cause this segment tooverfly the head means in a prescribed manner.
 15. The combination asrecited in claim 14, wherein such penetration is such as to form arelatively flat elliptical "dimple" in the passing segment above thehead means at height S_(t) therefrom.
 16. The combination as recited inclaim 12, wherein said "leading-face" portions form an air-foil surfaceof constant configuration to medium segments approaching from any anglein a given sector, being adapted to generate an "entry-dimple" in theapproaching medium segment of a prescribed height and configuration,this dimple located upstream of said head means.
 17. The combination asrecited in claim 13, wherein trailing-face portions of said foil meansare configured so as to minimize turbulance and flutter of the passingmedium and to quickly attenuate any disturbance therein.
 18. Improvedmagnetic recording apparatus adapted to operate upon one or morerotatable flexible circular record-disks disposed to be rotated along aprescribed relatively flat planar reference transducing plane, thisapparatus comprising transducer means including at least one transducerhead adapted to be thrust into and beyond said reference plane aprescribed penetration distance d_(p), but out of contact with saidrotating disk and in transducing relation therewith, said heads beingdisposed in a head mount curved at least along prescribed lead faceportions, in a single curvature adapted to induce the passing disk to bepulled toward itself; arm means designed to carry said transducing meansand adapted to so present said head, while supporting it rigid andstationary; and head support means adapted to support said transducermeans upon said arm means and including a lead-face portion exhibiting aprescribed regular curvature adapted to draw passing disk segmentstoward itself and thus generate a prescribed "entry-dimple" therein, theheight of this support means being adapted to help determine theprescribed penetration distance d_(p), and said lead-face configurationof said head-support means adapted to draw the passing disk segmentstoward itself to establish a prescribed minimal medium-height S_(t) andassociated "head-dimple" in the disks whereat one or more transducingcore gaps are disposed;said head thus being adapted to be presented inpenetrating, dimpling relation with prescribed radial sectors of saidrotating disk so as to invoke different serial stages of Bournoulliair-films characteristic of the lead-face curvature, these stagesincouding a "transducing film" above said head at the transducing zoneand an "entry film" upstream of this "transducing zone" at the"entry-dimple".
 19. A relatively rigid "multi-foil" transducer arrayadapted for operation with passing flexible media, inducing passingsegments of the media to "bend" and overfly itself, this array includingread/write means mounted in a head mount means adapted to induce themedia to pass along a prescribed read/write path defining a prescribed"transducing dimple" d_(t) above said read/write means, at a relativelyminiscule head spacing without instabilities and without need to movethe array toward or away from the media there, the array furtherincluding:arm means adapted to present this read/write means in rigidstationary relation with the media and at least one support meansdisposed in said arm means and so placed and so regularly curved alonglead-face portions as to generate a respective "approach-zone" upstreamof said read-write means, to thus gradually reduce head media spacingupstream of said dimple d_(t).
 20. The combination as recited in claim19, wherein said support means comprises a foil with a sphericallead-face plus a supporting pedestal arranged and adapted to bring thepassing medium segment closer, gradually, to said read/write means, andto thereby help pre-stabilize the passing medium.
 21. The combination asrecited in claim 19, wherein each said support means is adapted to drawpassing medium segments toward the head-mount means and so establish anentry-zone dimple d_(e) in the medium of prescribed configuration andheight above said read/write means.
 22. The combination as recited inclaim 19, wherein prescribed relief means are cut into the face of saidhead-mount means such as to control the configuration and height d_(t)of said dimple and so as to yield a prescribed minimum head-to-mediumspacing S_(t).